This invention relates to an apparatus and method for filtering fluids, particularly liquids, to remove suspended solids. More specifically, the invention concerns a filter apparatus in which liquids containing solids flow parallel to the filter screens, the solids are trapped in the screens, and are then removed by a flushing fluid which flows crosswise through the screens.
Filters are generally classified as disposable, or flushable (reusable). The apparatus of this invention utilizes a flushable filter. Backflushing is a common technique used to remove solids that accumulate on flushable filters. In the backflushing step, a fluid, such as air, steam, or a liquid, either with or without surfactants, is passed through the filter media in the reverse direction, to carry the solids away from the filter. But this technique has several drawbacks. For example, it's energy intensive, it's time consuming, and it's an inefficent process. The backflushing step is particularly undesirable from a time standpoint, because it increases the time span of the duty cycle, which is a measure of the total operating time during which filtering occurs. Another disadvantage of this technique is that it adds to the operating cost of a filtering operation.
The reverse osmosis (RO) process is one of the conventional techniques used in desalting sea water to obtain potable water, or commercially usable water. In a typical spiral wound RO module, non-woven screens made of polyethylene or polypropylene are used as spacers between the membranes. These screen members support the membrane and provide a flow path for the sea water to move through the module. The screen members also serve as a static mixer, which induces turbulence in the flowing fluid and thus reduces the concentration polarization. A disadvantage of the screen member spacers, however, is that they trap some of the collodial solids present in the feed water. These particles eventually settle down onto the mem-brane and cause a fouling problem. Attempts to solve the fouling problem led the applicants herein to the present invention.